The present invention relates generally to methods of enhancing display detection in passive sonar systems, and more particularly, to methods of enhancing display detection using harmonics of detected energy at several frequencies to improve the sensitivity of such passive sonar systems.
A detectable target typically radiates signals over a wide bandwidth. The energy contained in the radiated signals is thus spread over a wide spectrum of frequencies with only a fractional part of the total energy present at a given frequency. When uncorrelated noise and clutter is added to the radiated signals, it becomes more and more difficult to extract the target signals from the noisy signals.
Conventional detection circuitry operates on single frequencies or on single narrow frequency bands. The conventional detection circuitry only processes a band of frequencies from which only one signal frequency of the target signal is processed at any one time. As a result, only energy from a single frequency is used for target detection in conventional passive sonar systems, for example. This places a significant constraint on detection ability of conventional circuitry. When operating in a high noise environment, the resulting low signal to noise ratio of the target signal results in a generally unacceptable trade-off between no detection or unacceptable false alarm incidents.
Accordingly, it is the objective of the present invention to overcome the inherent bandwidth limitations of present target detection circuitry and to more fully utilize the total energy content of the radiated target signals. It is further an objective of the present invention to utilize the harmonics of a target signal to enhance the detectability thereof.